1. Field of the Invention
Processing residues in powder form which are charged with harmful substances, in most cases originating from combustion processes.
Dust deposition and gas purification have become more important in the context of environmental regulation. More stringent requirements are therefore also demanded of the concomitant further processing and storage of the harmful substances and their carriers.
The invention relates to the further development, improvement and simplification of separating off harmful substances to be treated separately from a complex particle mixture formed in combustion processes.
In particular, it relates to a process for separating off poisonous volatile chemical compounds from a mixture of solid particles having a particle size of up to 200 .mu.m.
2. Discussion of Background
Filter dust of industrial incineration plants, especially electrofilter dust, has a high percentage of polluting, enviromentally-unsafe harmful substances, some of which are poisonous. They include certain organic and in particular heavy metal compounds, for example of the elements Pb, Zn, Cd, Tl, Cu. Therefore, special regulations apply to such mixtures, and the filter dust must be considered and treated as special waste.
Currently, the treatment is carried out using 3 principles:
Agglomeration and compacting of the dust to give larger pieces by means of binders such as cement, asphalt etc., followed by ultimate disposal on a sanitary landfill (cf. "Behandlung und Verfestigung von Ruckstanden aus Kehrichtverbrennungsanlagen" (treatment and solidification of residues from waste incineration plants) Schriftenreihe Umweltschutz No. 62, Bundesamt fur Umweltschutz, Bern 1987). This gives a product whose mass is greater than that of the loose starting material. For this reason, the ultimate disposal becomes expensive and problematical due to the, in most cases, only limited availability of space.
Chemical treatment with acids. The heavy metal compounds are leached out using aqueous acids. The residue free of heavy metals is stored in a sanitary landfill, the acidic solutions containing heavy metals are further processed (cf. H. Vogg "Rauchgasreinigungsverfahren" (A process for the purification of fumes), talk given at the VDI seminar 43-32-02 "Abfallbehandlung und -ver-wertung durch Mullver-brennung" (treatment and utilization of waste by waste incineration) VDI, Dusseldorf 1986). However, these leaching out processes do not represent final solutions of the waste problem. The further treatment of the solutions containing heavy metals and their concentration is associated with a considerate energy consumption. New problems are created (waste water, pollution).
Thermomechanical separation by heating the dust charged with heavy metals in a gas stream, evaporation of the heavy metal compounds and mechanical removal of the solid suspended particles from the gas phase at high temperatures (hot gas cyclone, hot gas filter etc.). The heavy metal vapours are subsequently condensed in a cooler (cf. W. Weissweiler et al., "Anreicherung von Thallium- und Bleihalogeniden" (Concentration of thallium halides and lead halides), Staub, Reinhaltung der Luft, vol. 46, No. 3, p. 120-124, March 1986). The hot gas separators (cyclones, electrofilters, ceramic honey-comb filters etc.) have to operate isothermically at high temperatures (1000.degree. C. and more), which makes very high demands on their construction and operation. In addition, the removal of the fine dust (particle diameter less than 1 .mu.m), which, as the carrier of the heavy metal compounds, weighs too heavily in terms of its percentage, is hardly feasible using economical methods.